Catalyst for hydrocarbon steam cracking, method of preparing the same and method of preparing olefin by using the same

ABSTRACT

The present invention relates to a catalyst for hydrocarbon steam cracking for the production of light olefin, a preparation method of the catalyst and a preparation method of olefin by using the same. More precisely, the present invention relates to a composite catalyst prepared by mixing the oxide catalyst powder represented by CrZrjAkOx (0.5≦j≦120, 0≦k≦50, A is a transition metal, x is the number satisfying the condition according to valences of Cr, Zr and A, and values of j and k) and carrier powder and sintering thereof, a composite catalyst wherein the oxide catalyst is impregnated on a carrier, and a method of preparing light olefin such as ethylene and propylene by hydrocarbon steam cracking in the presence of the composite catalyst. The composite catalyst of the present invention has excellent thermal/mechanical stability in the cracking process, and has less inactivation rate by coke and significantly increases light olefin yield.

This application claims the benefit of the filing date of Korean PatentApplication No. 10-2007-0050975 filed on May 25, 2007 in the KoreanIntellectual Property Office, the disclosure of which is incorporatedherein in its entirety by reference.

TECHNICAL FIELD

The present invention relates to a catalyst for hydrocarbon steamcracking for the production of light olefin, a preparation method of thecatalyst and a preparation method of olefin by using the same. Moreprecisely, the present invention relates to a catalyst for hydrocarbonsteam cracking which gives improved yield of light olefin and hasthermal/mechanical stability at high temperature for the production oflight olefin by hydrocarbon steam cracking, a preparation method of thecatalyst and a preparation method of light olefin using the catalyst.

BACKGROUND ART

Important raw materials necessary for the production of petroleumproducts such as ethylene and propylene are prepared by hydrocarbonsteam cracking which is a major ingredient of natural gas or paraffincompounds such as naphtha and gas oil, at high temperature of at least800° C. in the presence of water vapor.

To increase the yield of ethylene or propylene from hydrocarbon steamcracking, it has been largely attempted to increase hydrocarbonconversion rate or to increase olefin selectivity. However, there is alimitation in increasing hydrocarbon conversion rate or olefinselectivity depending only on steam cracking. So, alternatives have beenproposed to increase olefin yield.

For example, using a catalyst for steam cracking was proposed as analternative for the improvement of ethylene and propylene yields fromhydrocarbon steam cracking. U.S. Pat. No. 3,644,557 describes thecatalyst composed of magnesium oxide and zirconium oxide, U.S. Pat. No.3,969,542 describes the catalyst containing calcium aluminate as a basiccomponent, U.S. Pat. No. 4,111,793 describes the manganese oxidecatalyst impregnated in zirconium oxide, European Patent Publication No.0212320 describes the iron catalyst impregnated in magnesium oxide, andU.S. Pat. No. 5,600,051 describes the catalyst composed of barium oxide,alumina and silica. PCT No. 2004/105939 describes a method using thecatalyst composed of potassium magnesium phosphate, silica and alumina.It has been known that these catalysts are acting as a heating mediumduring hydrocarbon steam cracking to increase olefin yield, but theincrease of olefin yield is not satisfactory compared with when aninactive carrier is used.

Russian Patent No. 1,011,236 describes the potassium vanadate catalystmodified with boron oxide carried in an alumina carrier. However, usingthe potassium vanadate catalyst or alkali metal oxide experiences notonly unsatisfactory improvement of olefin yield but also loss at hightemperature for hydrocarbon decomposition. That is, the components ofthe catalysts have low melting points and thus exist possibly in liquidphase in the inside of a high-temperature cracking reactor and they areeasily evaporated owing to the fast gas flow during the reaction,resulting in the loss of catalytic activity as reaction progresses.

U.S. Pat. No. 7,026,263 describes a method of using a hybrid catalystcomposed of molybdenum oxide, alumina, silica, silicalite and zirconiumoxide. The catalyst has an advantage of usability at low temperaturereaction, but at the same time has a disadvantage of difficulty indirect addition to the actual production line because it is used at avery low hydrocarbon superficial velocity. In addition, thermostabilityof such catalyst becomes very low at the reaction temperature of700˜800° C. or up, resulting in the loss of catalytic activity.

Most of the conventional cracking processes are performed at a highreaction temperature and with a high hydrocarbon superficial velocityand accompany the generation of a huge amount of coke. The generatedcoke has to be burned at a high temperature. To utilize a catalyst for along time under such a severe condition, the catalyst has to bethermally/physically stable with less transformation. However, the abovemethods and skills are in question of thermal/physical stability.

To prevent economical loss in the process of hydrocarbon steam crackingand to avoid complicated production processes, an excellent catalystwhich is capable of improving the yield of light olefin higher than aninactive carrier can do and is thermally/mechanically stable at hightemperature is required.

DISCLOSURE OF THE INVENTION

It is an object of the present invention, to overcome the above problemsof the conventional art, to provide a catalyst for hydrocarbon steamcracking which has excellent thermostability at high temperature andimproves olefin yield and selectivity from hydrocarbon steam crackingand at the same time has low inactivation rate by coke, more precisely acomposite catalyst prepared by sintering the mixture of the oxidecatalyst powder represented by CrZr_(j)A_(k)O_(x) and carrier powder,and a composite catalyst having the structure where the oxide catalystis impregnated on a carrier.

It is another object of the present invention to provide a method forpreparing a composite catalyst prepared by sintering the mixture of theoxide catalyst powder represented by CrZr_(j)A_(k)O_(x) and carrierpowder, and a composite catalyst having the oxide catalyst impregnatedon a carrier.

It is also an object of the present invention to provide a method forpreparing olefin by hydrocarbon steam cracking in the presence of thecatalyst.

The above objects and other objects of the present invention can beachieved by the following embodiments of the present invention.

The present invention is described in detail hereinafter.

To achieve the above objects, the present invention provides a catalystfor hydrocarbon steam cracking, which contains a composite catalystprepared by sintering the mixture of the oxide catalyst represented byCrZr_(j)A_(k)O_(x) (0.5≦j≦120, 0≦k≦50, A is a transition metal, x is thenumber satisfying the condition according to valences of Cr, Zr and A,and values of j and k) and carrier powder.

The present invention also provides a catalyst for hydrocarbon steamcracking which contains a composite catalyst having the oxide catalystrepresented by CrZr_(j)A_(k)O_(x) (0.5≦j≦120, 0≦k≦50, A is a transitionmetal, x is the number satisfying the condition according to valences ofCr, Zr and A, and values of j and k) impregnated on a carrier.

At this time, A of the oxide is one or more selected from the groupconsisting of Ti, Nb, Mo, V, Co, Ni, W, Fe and rare earth metals, and Tiis preferred.

The carrier is selected from the group consisting of alpha alumina,silica, silica-alumina, zirconium oxide, magnesium oxide, magnesiumaluminate, calcium aluminate, silicon carbide, aluminum titanate andzeolite, and silicon carbide is preferred.

The present invention provides a method for preparing a catalyst forhydrocarbon steam cracking comprising the following steps: (a) preparingan aqueous solution by mixing Cr containing compound and Zr containingcompound or Cr—Zr containing compound with water; (b) preparing a slurryby co-precipitation after adding ammonia water to the prepared aqueoussolution; (c) heat-refluxing or hydrothermal-treating the slurry; (d)preparing an oxide catalyst by filtering, drying and calcining theslurry; (e) preparing a composite catalyst by sintering the mixture ofthe oxide catalyst powder and carrier powder; (f) molding the compositecatalyst; and (g) sintering the molded composite catalyst.

The present invention also provides a method for preparing a catalystfor hydrocarbon steam cracking containing the following steps: (a)preparing an aqueous solution by mixing Cr containing compound and Zrcontaining compound or Cr—Zr containing compound with water; (b)impregnating a carrier in the prepared aqueous solution; and (c)preparing a composite catalyst containing the oxide component bysintering the impregnated carrier.

At this time, in the step (a), a metal compound containing one or moreselected from the group consisting of Ti, Nb, Mo, V, Co, Ni, W, Fe andrare earth metals, or the Cr containing compound or the Zr containingcompound or the Cr—Zr containing compound can additionally include oneor more selected from the group consisting of Ti, Nb, Mo, V, Co, Ni, W,Fe and rare earth metals, and preferably the compound contains Tiadditionally.

The carrier is selected from the group consisting of alpha alumina,silica, silica-alumina, zirconium oxide, magnesium oxide, magnesiumaluminate, calcium aluminate, silicon carbide, aluminum titanate andzeolite, and silicon carbide is preferred.

The present invention provides a method of preparing olefin containingthe step of hydrocarbon steam cracking in the presence of a catalystselected from the group consisting of a composite catalyst prepared bysintering the mixture of powder of the oxide catalyst represented byCrZr_(j)A_(k)O_(x) (0.5≦j≦120, 0≦k≦50, A is a transition metal, x is thenumber satisfying the condition according to valences of Cr, Zr and A,and values of j and k) and carrier powder, and a catalyst having theoxide catalyst impregnated on a carrier.

At this time, A of the oxide is one or more selected from the groupconsisting of Ti, Nb, Mo, V, Co, Ni, W, Fe and rare earth metals, and Tiis preferred.

The carrier is selected from the group consisting of alpha alumina,silica, silica-alumina, zirconium oxide, magnesium oxide, magnesiumaluminate, calcium aluminate, silicon carbide, aluminum titanate andzeolite, and silicon carbide is preferred.

Hereinafter, the present invention is described in detail.

The present inventors completed this invention by confirming that whenan oxide containing Cr and Zr or an oxide containing Cr and Zr and oneor more metals selected from the group consisting of Ti, Nb, Mo, V, Co,Ni, W, Fe and rare earth metals was used as a catalyst component andmolded with a carrier, the catalytic activity was increased comparedwith the conventional art, olefin yield was increased, inactivation rateby coke was reduced, possibility of deformation at high temperature waslowered owing to the excellent thermal/mechanical stability and theproblems of the conventional art such as decrease of hydrocarbondecomposing activity and unsatisfactory light olefin yield could beovercome.

As for the catalyst for hydrocarbon steam cracking of the presentinvention, two different types of catalysts can be used. One of the twois the composite catalyst prepared by sintering the mixture of the oxidecatalyst powder represented by CrZr_(j)A_(k)O_(x) and carrier powder,and the other of the two is the composite catalyst having the oxidecatalyst represented by CrZr_(j)A_(k)O_(x) impregnated on a carrier.

The catalytic component of the catalyst for hydrocarbon steam crackingis characteristically represented by formula 1.

CrZr_(j)A_(k)O_(x)  [Formula 1]

Wherein, 0.5≦j≦120, preferably 55≦j≦90, more preferably 70≦j≦90, 0≦k≦50,preferably, 5≦k≦30, more preferably 15≦k≦28, A is a transition metal, xis the number satisfying the condition according to valences of Cr, Zrand A, and values of j and k.

And, A contains one or more metals selected from the group consisting ofTi, Nb, Mo, V, Co, Ni, W, Fe and rare earth metals.

The catalyst for hydrocarbon steam cracking of the present invention cancontain a catalyst component represented by formula 2 which correspondsto when k of formula 1 is 0.

CrZr_(j)O_(x)  [Formula 2]

Wherein, 0.5≦j≦120, preferably 5≦j≦90, more preferably 70≦j≦90, and x isthe number satisfying the condition according to valences of Cr and Zrand j value.

When it is used for hydrocarbon steam cracking, the catalyst of thepresent invention not only increases the reaction yield but alsoimproves the selectivity of light olefin, specifically propylene, andmaintains thermo-stability.

When hydrocarbon steam cracking is performed at 800° C., the preferableratio of the ethylene/propylene is 1.5-1.7. When the reactiontemperature is increased more than 800° C., propylene selectivity beginsto decrease.

The method of preparing the catalyst for hydrocarbon steam cracking ofthe present invention characteristically contains the following steps:(a) preparing an aqueous solution by mixing Cr containing compound andZr containing compound or Cr—Zr containing compound with water; (b)preparing a slurry by co-precipitation after adding ammonia water to theprepared aqueous solution; (c) heat-refluxing or hydrothermal-treatingthe slurry; (d) preparing an oxide catalyst by filtering the slurry,drying and calcining thereof; (e) preparing a composite catalyst bysintering the mixture of the oxide catalyst powder and carrier powder;(f) molding the composite catalyst; and (g) sintering the moldedcomposite catalyst.

In step (a), an aqueous solution is prepared by mixing a metal compoundwith water.

The Cr containing compound and Zr containing compound or Cr—Zrcontaining compound can be a salt such as sulfate, nitrate, oxalate,halide or chloride, and nitrate is more preferred.

The metal compound such as Cr containing compound and Zr containingcompound or Cr—Zr containing compound can be further mixed with thethird metal compound. And herein, the third metal compound is a metalcompound which can be one or more compounds selected from the groupconsisting of Ti, Nb, Mo, V, Co, Ni, W, Fe and rare earth metals, andparticularly Ti, Ni and rare earth metals are preferred and Ti and Y aremore preferred.

The Cr containing compound, the Zr containing compound or the Cr—Zrcontaining compound are the third metal compound, which can include oneor more selected from the group consisting of Ti, Nb, Mo, V, Co, Ni, W,Fe and rare earth metals, and particularly Ti, Ni and rare earth metalsare preferred and Ti and Y are more preferred.

Each metal component of the third metal compound can be salt, acid,oxide, hydroxide or alkoxide, etc. If a metal component of the thirdmetal compound is an alkoxide precursor, the alkoxide is hydrolyzed inwater and educed as a solid salt. Therefore, a strong acid such asnitric acid is necessarily added to dissolve the salt.

After dissolving the metal component of the third metal compound inwater, this solution can be mixed with Cr and Zr aqueous solutions. Orthe metal component can be dissolved in water together with Cr and Zrprecursors.

The aqueous solution containing the components is heated and stirred at40-80° C., preferably 60-70° C. for at least one hour until all thecomponents are mixed completely.

In step (b), ammonia is added to the aqueous solution of step (a). PH ofthe solution is preferably regulated to 7-9, more preferably 8-8.5,followed by coprecipitation to prepare slurry.

In step (c), the slurry prepared in step (b) is heat-refluxed at thesame temperature as mentioned in step (a) for at least 12 hours orhydrothermal-treated via autoclave at 60-150° C.

In step (d), the slurry heat-refluxed or hydrothermal-treated in step(c) is filtered, dried and calcined to give a catalyst.

The drying is preferably performed at 120° C. for at least 2 hours.

The calcination herein is preferably performed at 750-1600° C. for atleast 4 hours. If the calcining temperature is maintained in the range,sintering is not hurry, so that catalytic activity is less reduced.

In step (e), the oxide catalyst powder represented by formula 1 orformula 2 prepared in step (d) is mixed with carrier powder, followed bysintering. The preferable content of the oxide catalyst component in thetotal weight of the composite catalyst is 0.5-50 weight %, which is thepreferable content facilitating hydrocarbon steam cracking. If thecontent is less than 0.5 weight %, the oxide catalyst component cannotbe fully functioning as a catalyst. In the meantime, if the content ismore than 50 weight %, the strength of the catalyst is reduced. A bindercan be additionally added during the mixing of the oxide catalystcomponent and a carrier.

The carrier herein can be any conventional carrier selected from thegroup consisting of alpha alumina, silica, silica-alumina, zirconiumoxide, magnesium oxide, magnesium aluminate, calcium aluminate, siliconcarbide, aluminum titanate and zeolite, and silicon carbide ispreferred. When silicon carbide is used as a carrier, the precursors ofsilicon carbide, silicon and carbon, can be mixed with the oxidecatalyst component. At this time, silicon and carbon, the precursors,are changed into silicon carbide during the sintering process of step(g).

In step (f), the composite catalyst of step (e) is molded in a specificform. For the molding, compression molding or extrusion molding isperformed.

In step (g), the molded product in a specific shape, prepared in step(f), is sintered. The molded product of step (f) becomes smaller involume during the sintering, resulting in a composite catalyst having aright size, density and surface area. The sintering is performed at thetemperature of at least 1200° C. for at least 2 hours.

The composite catalyst finished with the sintering above preferably hasthe density of 0.5˜3.5 g/cm³, the surface area of up to 50 m²/g and thecompressive strength of at least 1000N.

Another method of preparing the catalyst for hydrocarbon steam crackingof the present invention comprises the following steps: (a) preparing anaqueous solution by mixing Cr containing compound and Zr containingcompound or Cr—Zr containing compound with water; (b) impregnating acarrier in the prepared aqueous solution; and (c) preparing a compositecatalyst containing the oxide component by sintering the impregnatedcarrier. As a result, the catalyst harboring the oxide catalystcomponent represented by formula 1 or formula 2, which is a compositecatalyst, is prepared.

In step (a), an aqueous solution is prepared by mixing a metal compoundwith water.

The Cr containing compound and Zr containing compound or Cr—Zrcontaining compound can be a salt such as sulfate, nitrate, oxalate,halide or chloride, and nitrate is more preferred.

The metal compound such as Cr containing compound and Zr containingcompound or Cr—Zr containing compound can be further mixed with thethird metal compound. And herein, the third metal compound is a metalcompound which can be one or more compounds selected from the groupconsisting of Ti, Nb, Mo, V, Co, Ni, W, Fe and rare earth metals, andparticularly Ti, Ni and rare earth metals are preferred and Ti and Y aremore preferred.

The Cr containing compound, Zr containing compound or Cr—Zr containingcompound is the third metal compound, which can includes one or moreselected from the group consisting of Ti, Nb, Mo, V, Co, Ni, W, Fe andrare earth metals, and particularly Ti, Ni and rare earth metals arepreferred and Ti and Y are more preferred.

Each metal component of the third metal compound can be salt, acid,oxide, hydroxide or alkoxide, etc. If a metal component of the thirdmetal compound is an alkoxide precursor, the alkoxide is hydrolyzed inwater and educed as a solid salt. Therefore, a strong acid such asnitric acid is necessarily added to dissolve the salt.

After dissolving the metal component of the third metal compound inwater, this solution can be mixed with Cr and Zr aqueous solutions. Orthe metal component can be dissolved in water together with Cr and Zrprecursors.

The aqueous solution containing the components is heated and stirred at40-80° C., preferably 60-70° C. for at least one hour until all thecomponents are mixed completely.

In step (b), the aqueous solution is impregnated on a carrier byincipient wetness impregnation or liquid impregnation, followed bydrying (at 120° C. for at least 10 hours) to prepare a carrier loadedwith a catalyst precursor.

Calcination is preferably performed at 800-1400° C. for at least 6hours.

The composite catalyst finished with calcining preferably contains theoxide catalyst component of 0.5-30 weight % by the total weight of thecomposite catalyst for the successful hydrocarbon steam cracking. If thecontent is less than 0.5 weight %, the catalytic activity is in doubt.If the content is more than 30 weight %, the catalytic effect isinefficient.

At this time, the carrier can be any conventional carrier selected fromthe group consisting of alpha alumina, silica, silica-alumina, zirconiumoxide, magnesium oxide, magnesium aluminate, calcium aluminate, siliconcarbide, aluminum titanate and zeolite. Among these carriers, siliconcarbide having compressive strength of at least 1000 N is morepreferred.

The method of preparing light olefin of the present invention ischaracterized by using the catalyst for hydrocarbon steam crackingprepared by the above method for hydrocarbon steam cracking.

The light olefin of the present invention indicates olefin having up to4 carbons, particularly exemplified by ethylene and propylene.

The hydrocarbon steam cracking for the production of light olefin ispreferably performed at 600-1000° C., weight ratio of watervapor/hydrocarbon of 0.3-1.0 and space velocity (LHSV) of 1-20 hr⁻¹.

In this reaction, a fixed bed reactor, a fluidized bed reactor or amobile phase reactor can be used. In particular, when a fixed bedreactor is used, a round shaped or pellet catalyst can be used, but atthis time, differential pressure in the catalyst layer becomes bigger,which is a problem. To overcome this problem, a catalyst is preferablymolded in the shape of Raschig or in any other specific shapes toincrease porosity in the catalyst layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The application of the preferred embodiments of the present invention isbest understood with reference to the accompanying drawings, wherein:

FIG. 1 illustrates the ratios of the reaction products methane/propyleneproduced from hydrocarbon steam cracking reaction of the presentinvention by using different catalysts which are the composite catalystof Example 9 and silicon carbide of Comparative Example 4.

FIG. 2 illustrates the ratios of the reaction productsethylene/propylene produced from hydrocarbon steam cracking reaction ofthe present invention by using different catalysts which are thecomposite catalyst of Example 9 and silicon carbide of ComparativeExample 4.

FIG. 3 illustrates the yields of ethylene and propylene, the productsfrom hydrocarbon steam cracking reaction of the present invention, overthe driving time when the composite catalyst of Example 9 is used.

BEST MODE FOR CARRYING OUT THE INVENTION

Practical and presently preferred embodiments of the present inventionare illustrative as shown in the following Examples.

However, it will be appreciated that those skilled in the art, onconsideration of this disclosure, may make modifications andimprovements within the spirit and scope of the present invention.

Example 1

A mixed aqueous solution was prepared by dissolving 2.96 g of chromenitrate hydrate and 8.93 g of zirconia nitrate hydrate in water. Ammoniawater was dropped slowly to the prepared mixed aqueous solution, duringwhich pH was regulated as 8, followed by coprecipitation and thenheat-refluxing for 12 hours. The coprecipitated aqueous solution wasfiltered and washed with water. The catalyst was separated therefrom.Moisture was eliminated by drying the catalyst in a drier. The driedcatalyst was calcined at 800° C. for 6 hours in air atmosphere.

The catalyst produced above was confirmed to have the composition ofCrZr₅O_(x).

Example 2

An experiment was performed by the same manner as described in Example 1except that the calcination was performed at 1200° C.

Example 3

2.68 g of titanium isopropoxide was dissolved in water and nitric acidwas slowly dropped in the solution with stirring until it came clear.12.35 g of zirconia nitrate hydrate and 0.24 g of chrome nitrate hydratewere added thereto, resulting in the mixed aqueous solution. Ammoniawater was dropped slowly to the mixed aqueous solution, during which pHwas regulated as 8, followed by coprecipitation and then heat-refluxingfor 12 hours. The coprecipitated aqueous solution was filtered andwashed with water. The catalyst was separated therefrom. Moisture waseliminated by drying the catalyst in a drier. The dried catalyst wascalcined at 800° C. for 6 hours in air atmosphere.

The catalyst produced above was confirmed to have the composition ofCrZr_(83.3)Ti_(16.7)O_(x).

Example 4

An experiment was performed by the same manner as described in Example 3except that the calcination was performed at 1200° C.

Example 5

The catalyst prepared in Example 3 was used for the hexane contactingsteam cracking for 5 hours under the same conditions as described in thefollowing Experimental Example and then the catalyst was recovered andregenerated by burning coke for 6 hours in air atmosphere.

Example 6

The catalyst powder prepared in Example 3 was mixed with the siliconcarbide powder of Comparative Example 3, followed by vacuum sintering.The catalyst finished with the sintering according to the procedurecontained CrZr_(83.3)Ti_(16.7)O_(x) by 5, 10 and 15 weight % for theweight of silicon carbide.

Example 7

The catalyst powder prepared in Example 3 was mixed with silicon andcarbon powder, followed by vacuum sintering. The catalyst finished withthe sintering according to the procedure containedCrZr_(83.3)Ti_(16.7)O_(x) by 5, 10 and 15 weight % for the weight ofsilicon carbide.

Example 8

2.68 g of titanium isopropoxide was dissolved in water and nitric acidwas slowly dropped in the solution with stirring until it came clear.12.35 g of zirconia nitrate hydrate and 0.24 g of chrome nitrate hydratewere added thereto, resulting in the mixed aqueous solution. The mixedaqueous solution was impregnated in a silicon carbide carrier byincipient wetness impregnation. The catalyst prepared by impregnating acatalyst precursor solution in silicon carbide was dried in a drier,followed by calcining at 800° C. for 6 hours. The catalyst finished withthe calcination according to the above procedure containedCrZr_(83.3)Ti_(16.7)O_(x) by 10 weight % for the weight of siliconcarbide.

Comparative Example 1

500 μm sized α-alumina having 99.5% purity was used herein.

Comparative Example 2

An aqueous solution was prepared by dissolving 15.87 g of magnesiumnitrate hydrate, 4 g of potassium hydroxide and 7.12 g of ammoniumphosphate in water. The mixed aqueous solution was dried by vacuumdistillation using a vacuum evaporator to obtain a catalyst. Thecatalyst was dried in a drier, followed by calcining at 1100° C. for 6hours.

The catalyst produced above was confirmed to have the composition ofKMgPO₄.

Comparative Example 3

500 μm sized silicon carbide having 99.5% purity was used herein.

Experimental Example 1

The catalysts prepared in Examples 1-8 and Comparative Example 1-3 wereused for hydrocarbon steam cracking according to the following methods.

Hexane was used as hydrocarbon. A quartz tube of ¼″ in external diameterwas filled with the catalyst up to 5 cm in height and the reactiontemperature was maintained as 750° C. The injection ratio of hexane towater was 2:1 and the flow speed of hexane was adjusted to LHSV of 5hr⁻¹. Hexane and water were injected by using a syringe pump. Hexane andwater were evaporated respectively at 400° C. and at 500° C. using avaporizer to be ready for the contact with the catalyst layer. At thistime, contact between the gas and the catalyst layer was made when thetwo gases were well mixed. The product discharged from the rector wasquantified by gas chromatography and the yield of the product wascalculated according to the following Mathematical Formula 1.

Yield of the product(weight %)=weight of the product/weight of theinjected hexane×100  [Mathematical Formula 1]

Example 9

The catalyst powder prepared in Example 3 was mixed with silicon carbidepowder, followed by vacuum sintering. The catalyst finished with thesintering according to the procedure contained CrZr_(83.3)Ti_(16.7)O_(x)by 10 weight % for the weight of silicon carbide and had density of 1.34g/cm³.

Comparative Example 4

Silicon carbide having 99.5% purity and density of 2.6 g/cm³ was usedherein.

Experimental Example 2

Ethylene and propylene were produced using the catalysts prepared inExample 9 and Comparative Example 4 by the following method. Naphtha wasused as hydrocarbon for hydrocarbon steam cracking and the compositionand physical property of the naphtha used herein are shown in Table 1.

TABLE 1 Physical Property Initial Terminal Composition (weight %)Density boiling boiling Aromatic (g/cc) point (° C.) point (° C.)n-paraffin l-paraffin Naphthene compound 0.675 30.9 160.7 39.5 38.9 15.36.3

Naphtha and water were added to the reactor by using a metering pump. Atthis time, the addition weight ratio of naphtha to water was 2:1. Theflow rate of naphtha was adjusted to 10 hr⁻¹ of LHSV. Naphtha and wateradded to the reactor were mixed after passing through the evaporator andthen passed through the first preheater heated at 550° C., followed bypassing through the second preheater heated at 650° C. The mixture wasthen injected in the reactor (length: 300 cm, diameter: 4.3 cm) filledwith the catalyst.

The reactor was heated by electric furnace. The water vapor-naphthamixture passed through the second preheater was cracked while it passedthrough the reactor. The outlet temperature of the reactor (reactiontemperature) was regulated between 740˜820° C. but maintained at 800° C.upon completion of the reaction. The reaction products passed throughtwo condensers connected serially, during which water and heavy oil werecondensed and separated as a liquid phase and the remaining gas phasemixture was analyzed by gas chromatography connected online, followed byelimination. The naphtha cracking procedure continued for 120 hours andcoke was burned at 800° C. in water vapor-air atmosphere to regeneratethe catalyst. The naphtha cracking-coke burning process repeated twomore times, completing the three-cycle reaction in total. The yield ofethylene was calculated by the following Mathematical Formula 2 and theyield of another product (propylene) was calculated by the same method.

Yield of ethylene(weight %)=amount of produced ethylene/amount ofinjected naphtha×100  [Mathematical Formula 2]

TABLE 2 calcining Conversion temperature Yield (weight %) rateComposition (° C.) Ethylene Propylene Ethylene + propylene (weight %)Example 1 CrZr₅O_(x) 800 23.04 19.30 42.34 73.93 2 CrZr₅O_(x) 1200 22.4815.84 38.32 61.21 3 CrZr_(83.3)Ti_(16.7)O_(x) 800 24.39 20.18 44.5775.12 4 CrZr_(83.3)Ti_(16.7)O_(x) 1200 24.10 18.07 42.17 67.69 5CrZr_(83.3)Ti_(16.7)O_(x) 800 23.92 19.60 43.52 72.70 Comparative 1α-alumina — 22.27 14.30 36.57 60.42 Example 2 KMgPO₄ 1100 23.36 14.8038.16 59.94

As shown in Table 2, the catalyst of the present invention which is theoxide catalyst containing Cr and Zr (Example 1) exhibited approximately14 weight % increased conversion rate of hexane decomposition, comparedwith Comparative Example 1 using α-alumina, and approximately 6 weight %increased olefin yield owing to its Cr—Zr oxide complex structureproviding catalytic active site that favors the catalytic activity inhydrocarbon steam cracking. The oxide catalyst containing Cr and Zr ofthe present invention is more effective in hydrocarbon cracking toproduce light olefin, in particular to produce propylene, than theconventional catalyst KMgPO₄ of Comparative Example 2.

The catalyst prepared in Example 3 by calcining the oxide catalystcontaining Cr and Zr and a transition metal such as Ti exhibited alittle increased catalytic activity and as a result increased lightolefin selectivity and yield thereof. Compared with the catalyst ofExample 1, the conversion rate of hexane decomposition was approximately1.2 weight % increased and olefin yield was also approximately 2.2weight % increased.

Hydrocarbon steam cracking was performed at about 800° C. but thecatalyst could be exposed on much higher temperature temporarily orlocally by hot-spot generated during the burning process to eliminatecoke generated on the inside wall of the reactor or the surface of thecatalyst. Therefore, a catalyst having an excellent thermostability isrequired so as to maintain its catalytic activity at high temperature ofat least 1000° C.

The catalyst of Example 2 prepared by calcining the oxide catalystcontaining Cr and Zr, the catalytic components of the present invention,at 1200° C. exhibited reduced hexane decomposing activity and as aresult light olefin yield was reduced approximately 4 weight %, comparedwith the catalyst of Example 1. However, compared with α-alumina ofComparative Example 1, this catalyst exhibited still high catalyticactivity.

The catalyst of Example 4 prepared by mixing with Cr and Zr andadditionally Ti and calcining at 1200° C. exhibited a little reducedcatalytic activity compared with the catalyst of Example 3, but theselectivity of light olefin was excellent. Thus, the yield of olefin was5.6 weight % higher than that of the reaction using α-alumina ofComparative Example 1. The catalyst of Example 5, regenerated by burningcoke generated on the surface of the catalyst after hydrocarbon steamcracking at high temperature maintained its catalytic activity. Theoxide catalyst containing Cr and Zr and Ti was confirmed to be verystable at high temperature of at least 1200° C. and at the same time atlow temperature of up to 1000° C. and has excellent catalytic activity.

TABLE 3 Yield (weight %) Ethylene + Conversion Composition EthylenePropylene propylene rate (weight %) Example 6 5% 23.01 14.91 37.91 60.22CrZr_(83.3)Ti_(16.7)O_(x) + SiC 10% 23.89 15.62 39.52 62.17CrZr_(83.3)Ti_(16.7)O_(x) + SiC 15% 24.89 15.95 40.83 64.1CrZr_(83.3)Ti_(16.7)O_(x) + SiC Example 7 5% 22.26 13.6 35.86 56.26CrZr_(83.3)Ti_(16.7)O_(x) + Si + C 10% 22.34 14.06 36.4 57.51CrZr_(83.3)Ti_(16.7)O_(x) + Si + C 15% 22.82 14.48 37.3 59.59CrZr_(83.3)Ti_(16.7)O_(x) + Si + C Example 8 10% 22.87 14.95 37.82 60.32CrZr_(83.3)Ti_(16.7)O_(x) + SiC Comparative SiC 21.34 13.73 35.06 55.86Example 3

As shown in Table 3, the composite catalyst containing the oxidecatalyst component having the composition of CrZr_(83.3)Ti_(16.7)O_(x)and the carrier silicon carbide of Example 6 exhibited improved lightolefin (ethylene, propylene) yield, compared with the silicon carbide ofComparative Example 3 not having the active site. As the content ofCrZr_(83.3)Ti_(16.7)O_(x) increased, light olefin yield increased. Whenthe content of CrZr_(83.3)Ti_(16.7)O_(x) was increased up to 15 weight%, light olefin yield was increased 5.8 weight %. The catalyst ofExample 7 prepared by mixing the oxide having the composition ofCrZr_(83.3)Ti_(16.7)O_(x) and silicon and carbon exhibited a littleincreased light olefin yield compared with the catalyst of ComparativeExample 3 but showed lower conversion rate and light olefin yield thanthe catalyst of Example 6. Therefore, it is suggested that siliconcarbide carrier is preferred to prepare a composite catalyst with theoxide having the composition of CrZr_(83.3)Ti_(16.7)O_(x) and siliconcarbide.

The yield of light olefin was increased not only by using the catalystprepared from the mixture of the oxide having the composition ofCrZr_(83.3)Ti_(16.7)O_(x) and silicon carbide and sintering thereof butalso by using the catalyst prepared by impregnating the catalystcomponent in a molded silicon carbide carrier. The catalyst of Example8, in which 10 weight % of CrZr_(83.3)Ti_(16.7)O_(x) was impregnated inthe silicon carbide carrier, exhibited higher olefin yield than thecatalyst of Example 7 (compared with equal amount of each catalyst) butlower olefin yield than the catalyst of Example 6. The compositecatalysts of examples demonstrated high catalytic activity andselectivity even after calcining at high temperature of at least 1200°C. In particular, the composite catalyst of Example 6 exhibitedexcellent light olefin selectivity without any catalytic activity loss.

TABLE 4 Reaction Yield (weight %) Ethylene/ Temperature Ethylene +propylene Cycle No. (° C.) Ethylene Propylene propylene ratio Example 91 740 16.8 15.09 31.89 1.11 1 780 25.26 17.25 42.51 1.46 1 800 27.0616.78 43.84 1.61 1 820 31.89 14.83 46.72 2.15 2 800 26.16 16.32 42.481.60 Comparative 1 740 15.94 14.34 30.28 1.11 Example 4 1 780 22.9714.05 37.02 1.63 1 800 26.32 13.56 39.88 1.94 1 820 29.79 12.41 42.2 2.4

As shown in Table 4, the composite catalyst of Example 9 prepared bymixing the oxide catalyst component having the composition ofCrZr_(83.3)Ti_(16.7)O_(x) and the carrier silicon carbide could increaselight olefin (ethylene, propylene) yield up to 1.5-4.5 weight %,compared with silicon carbide not having the active site used inComparative Example 4. As reaction temperature was raised, light olefinyield increased and the catalyst was more effective in producingpropylene than in producing ethylene. However, when reaction temperaturewas at least 800° C., propylene yield began to decrease. Therefore, todrive propylene at the best mode, temperature was preferably set at780˜800° C.

In the cracking process, the ratios of methane/propylene andethylene/propylene are indexes indicating not only the toughness of thecracking process but also the light olefin selectivity.

As shown in Table 4, when the cracking was performed at 800° C., theratio of ethylene/propylene of Example 9 was 1:61 and that ofComparative Example 4 was 1.94. That is, the ratio of ethylene/propylenebecame lower when the composite catalyst of Example 9 was used, comparedwith when silicon carbide was used in Comparative Example 4, suggestingthat the catalyst of Example 9 was more effective in increasingpropylene selectivity.

As shown in FIG. 1 and FIG. 2, the composite catalyst of Example 9exhibited lower methane/propylene ratio and ethylene/propylene ratiothan silicon carbide of Comparative Example 4 showed. That is, highpropylene ratio in the equal amount of produced methane suggests thatpropylene selectivity increases. Low ethylene/propylene ratio indicatesthat this catalyst favors propylene production. The silicon carbide ofComparative Example 4 has no such active site and only induced cracking.In the meantime, the composite catalyst of Example 9 has the effect ofincreasing ethylene and propylene yields, particularly favors theimprovement of propylene selectivity.

In the high temperature naphtha decomposition, coke deposition on thesurface of a catalyst and inside of the reactor is unavoidable. So, thedecrease of olefin yield by coke deposition during the cracking processis necessarily expected but when the composite catalyst of Example 9prepared by the method of the present invention is used for thereaction, catalytic activity is almost maintained without loss for thewhole operating time of 120 hours, as shown in FIG. 3. This is becausecoke deposition on silicon carbide used as a carrier is hardly observedand the coke deposition on the wall of the reactor is also significantlyreduced.

Hydrocarbon steam cracking is performed at around 800° C. But, toeliminate coke generated on the surface of the catalyst or inside wallof the reactor, burning is necessary, during which the catalyst can beexposed temporarily or locally on very high temperature by hot spot. So,a catalyst having excellent thermostability is highly recommended tomaintain catalytic activity during hydrocarbon steam cracking beingperformed at the temperature of at least 1000° C. The composite catalystof Example 9 prepared by the method of the present invention recoveredone-cycle of catalytic activity even after being regenerated by burningcoke generated on the surface of the catalyst at high temperature afternaphtha decomposition. After completing 3 cycles, the composite catalystshowed no thermal/physical changes and maintained the primary mechanicalstrength.

The composite catalyst of Example 9 was confirmed to be stable at up to1000° C. and at the same time at high temperature of at least 1200° C.and has low inactivation rate but excellent catalytic activity.

INDUSTRIAL APPLICABILITY

As explained hereinbefore, the catalyst for hydrocarbon steam crackingof the present invention has excellent thermal/mechanical stability athigh temperature, has low inactivation rate by coke, and has the effectof improving light olefin selectivity and yield.

Those skilled in the art will appreciate that the conceptions andspecific embodiments disclosed in the foregoing description may bereadily utilized as a basis for modifying or designing other embodimentsfor carrying out the same purposes of the present invention. Thoseskilled in the art will also appreciate that such equivalent embodimentsdo not depart from the spirit and scope of the invention as set forth inthe appended claims.

1. A catalyst for hydrocarbon steam cracking comprising a compositecatalyst prepared by mixing an oxide catalyst powder represented byCrZr_(j)A_(k)O_(x)(0.55≦j≦120, 0≦k≦50, A is a transition metal, x is thenumber satisfying the condition according to valences of Cr, Zr and A,and values of j and k) and a carrier powder and sintering the same. 2.The catalyst for hydrocarbon steam cracking according to claim 1,wherein the composite catalyst has the density of 0.5˜3.5 g/cm³, thesurface area up to 50 m²/g and the compressive strength of at least 1000N.
 3. The catalyst for hydrocarbon steam cracking according to claim 1,wherein the A of the oxide is one or more selected from the groupconsisting of Ti, Nb, Mo, V, Co, Ni, W and Fe.
 4. The catalyst forhydrocarbon steam cracking according to claim 1, wherein the A of theoxide is Ti.
 5. The catalyst for hydrocarbon steam cracking according toclaim 1, wherein the carrier is selected from the group consisting ofalpha alumina, silica, silica-alumina, zirconium oxide, magnesium oxide,magnesium aluminate, calcium aluminate, silicon carbide, aluminumtitanate and zeolite.
 6. The catalyst for hydrocarbon steam crackingaccording to claim 1, wherein the carrier is silicon carbide.
 7. Thecatalyst for hydrocarbon steam cracking according to claim 1, whereinthe steam cracking is performed in the presence of the catalyst forhydrocarbon steam cracking at 800° C. and at this time the ratio ofproducts ethylene/propylene is 1.5-1.7.
 8. A catalyst for hydrocarbonsteam cracking comprising a composite catalyst prepared by impregnatingan oxide catalyst represented by CrZr_(j)A_(k)O_(x) (0.55≦j≦120, 0≦k≦50,A is a transition metal, x is the number satisfying the conditionaccording to valences of Cr, Zr and A, and values of j and k) on acarrier.
 9. The catalyst for hydrocarbon steam cracking according toclaim 8, wherein the A of the oxide is one or more selected from thegroup consisting of Ti, Nb, Mo, V, Co, Ni, W and Fe.
 10. The catalystfor hydrocarbon steam cracking according to claim 8, wherein the A ofthe oxide is Ti.
 11. The catalyst for hydrocarbon steam crackingaccording to claim 8, wherein the carrier is selected from the groupconsisting of alpha alumina, silica, silica-alumina, zirconium oxide,magnesium oxide, magnesium aluminate, calcium aluminate, siliconcarbide, aluminum titanate and zeolite.
 12. The catalyst for hydrocarbonsteam cracking according to claim 8, wherein the carrier is siliconcarbide.
 13. The catalyst for hydrocarbon steam cracking according toclaim 8, wherein the steam cracking is performed in the presence of thecatalyst for hydrocarbon steam cracking at 800° C. and at this time theratio of the products ethylene/propylene is 1.5-1.7.
 14. A method ofpreparing a catalyst for hydrocarbon steam cracking comprising the stepsof: (a) preparing an aqueous solution by mixing Cr containing compoundand Zr containing compound or Cr—Zr containing compound with water; (b)preparing a slurry by co-precipitation after adding ammonia water to theaqueous solution; (c) heat-refluxing or hydrothermal-treating theslurry; (d) preparing an oxide catalyst by filtering, drying andcalcining the slurry; (e) preparing a composite catalyst by sintering amixture of a powder of the oxide catalyst and a carrier powder; (f)molding the composite catalyst; and (g) sintering the molded compositecatalyst.
 15. The method of preparing a catalyst for hydrocarbon steamcracking according to claim 14, wherein one or more metal compoundsselected from the group consisting of Ti, Nb, Mo, V, Co, Ni, W and Feare additionally added in the step (a) or the Cr containing compound orZr containing compound or Cr—Zr containing compound additionally containone or more compounds selected from the group consisting of Ti, Nb, Mo,V, Co, Ni, W and Fe.
 16. The method of preparing a catalyst forhydrocarbon steam cracking according to claim 14, wherein a metalcompound including Ti is additionally added in the step (a), or the Crcontaining compound or Zr containing compound or Cr—Zr containingcompound additionally include Ti.
 17. The method of preparing a catalystfor hydrocarbon steam cracking according to claim 14, wherein thecalcinations is performed at 750-1600° C. for at least 4 hours.
 18. Themethod of preparing a catalyst for hydrocarbon steam cracking accordingto claim 14, wherein the carrier is selected form the group consistingof alpha alumina, silica, silica-alumina, zirconium oxide, magnesiumoxide, magnesium aluminate, calcium aluminate, silicon carbide, aluminumtitanate and zeolite.
 19. The method of preparing a catalyst forhydrocarbon steam cracking according to claim 14, wherein the carrier issilicon carbide.
 20. The method of preparing a catalyst for hydrocarbonsteam cracking according to claim 14, wherein the content of the oxidecatalyst is 0.5-50 weight % by the total weight of the compositecatalyst.
 21. The method of preparing a catalyst for hydrocarbon steamcracking according to claim 14, wherein the sintering is performed at1200° C. or up for at least 2 hours.
 22. A method of preparing acatalyst for hydrocarbon steam cracking comprising the steps of: (a)preparing an aqueous solution by mixing Cr containing compound and Zrcontaining compound or Cr—Zr containing compound with water; (b)impregnating a carrier in the aqueous solution; and (c) preparing acomposite catalyst containing an oxide component by calcining theimpregnated carrier.
 23. The method of preparing a catalyst forhydrocarbon steam cracking according to claim 22, wherein one or moremetal compounds selected from the group consisting of Ti, Nb, Mo, V, Co,Ni, W and Fe are additionally added in the step (a), or the Crcontaining compound or Zr containing compound or Cr—Zr containingcompound additionally contain one or more compounds selected from thegroup consisting of Ti, Nb, Mo, V, Co, Ni, W and Fe.
 24. The method ofpreparing a catalyst for hydrocarbon steam cracking according to claim22, wherein the metal compound including Ti is additionally added in thestep (a), or the Cr containing compound or the Zr containing compound orthe Cr—Zr containing compound additionally include Ti.
 25. The method ofpreparing a catalyst for hydrocarbon steam cracking according to claim22, wherein the carrier is selected form the group consisting of alphaalumina, silica, silica-alumina, zirconium oxide, magnesium oxide,magnesium aluminate, calcium aluminate, silicon carbide, aluminumtitanate and zeolite.
 26. The method of preparing a catalyst forhydrocarbon steam cracking according to claim 22, wherein the carrier issilicon carbide.
 27. The method of preparing a catalyst for hydrocarbonsteam cracking according to claim 22, wherein the calcination isperformed at 800-1400° C. for at least 6 hours.
 28. The method ofpreparing a catalyst for hydrocarbon steam cracking according to claim22, wherein the content of the oxide catalyst is 0.5-50 weight % by thetotal weight of the composite catalyst.
 29. A method of preparing olefincomprising the step of hydrocarbon steam cracking in the presence of acatalyst selected from the group consisting of a composite catalystprepared by sintering a mixture of a powder of the oxide catalystrepresented by CrZr_(j)A_(k)O_(x)(0.5≦j≦120, 0≦k≦50, A is a transitionmetal, x is the number satisfying the condition according to valences ofCr, Zr and A, and values of j and k) and a carrier powder; and acomposite catalyst having the oxide catalyst impregnated on a carrier.30. The method of preparing olefin according to claim 29, wherein the Aof the oxide is one or more selected from the group consisting of Ti,Nb, Mo, V, Co, Ni, W and Fe.
 31. The method of preparing olefinaccording to claim 29, wherein the A of the oxide is Ti.
 32. The methodof preparing olefin according to claim 29, wherein the carrier isselected form the group consisting of alpha alumina, silica,silica-alumina, zirconium oxide, magnesium oxide, magnesium aluminate,calcium aluminate, silicon carbide, aluminum titanate and zeolite. 33.The method of preparing olefin according to claim 29, wherein thecarrier is silicon carbide.
 34. The method of preparing olefin accordingto claim 29, wherein the steam cracking temperature is 600-1000° C., theweight ratio of water vapor/hydrocarbon is 0.3-1.0 and the spacevelocity (LHSV) is 1-20 hr⁻¹.
 35. The method of preparing olefinaccording to claim 29, wherein the steam cracking is performed by usinga reactor selected from the group consisting of a fixed bed reactor, afluidized bed reactor and a mobile phase reactor.